Water quality indices and multivariate statistical analysis of urban groundwater in semi-arid Sokoto Basin, Northwestern Nigeria

Abstract

Drinking water is limited in quantity and quality in fast-growing cities in developing countries. Water quality has been impacted by competing demands by industry, municipal supplies, and agriculture. This study investigates groundwater quality in three urban centres in the semiarid Sokoto Basin, North-Western Nigeria. The study employed in situ and laboratory analyses and 30 water samples were analysed. Physical parameters (pH, Temp., EC, and TDS) were analysed using hand-held metres during sampling. Separate water samples were collected to determine chemical parameters (Ca2+, Cu2+, Fe3+, K+, Mg2+, Na+, Zn2+, Cl-, CO32-, HC03-, NO3-, PO43- and SO42-). Results indicate that most sampling locations in the study area have good quality water, 10% of sampling locations fell in the poor water class based on the Water Quality Index (WQI). Iron (Fe3+) and NO3- were the major pollutants and occurred at concentrations above (WHO, 2011) and (NSDWQ, 2007) reference guidelines. Hydrogeochemical facies revealed Ca–Mg–SO4–Cl and Ca–Cl water types. There is no dominant water type in the cation triangle, though the Cl-water type is formed in an anion triangle. Rock weathering controls groundwater quality primarily, as revealed by multivariate statistical analysis and the Gibbs model. The HCA results showed that, though clusters 1 and 2 can be classified as NO3- polluted boreholes, the boreholes ARG7 and ARG10 revealed relatively different groundwater compositions. The study, therefore, concludes that despite the increased urbanisation in the semiarid Sokoto basin, there is little evidence of groundwater quality deterioration. The WQI and multivariate statistics provide a framework for researchers who may require more accurate results while considering multiple groundwater quality parameters. This approach can be applied in other urban centres, mainly in arid and semiarid environments.